The present invention relates to an imaging system which utilizes a plurality of gradient index lens arrays to transmit an image of a document at an object plane to an image plane at various magnifications. More particularly, the invention relates to an optical system which extends the magnification range of a given system by anamorphically enlarging or reducing the image transmitted at the image plane at a particular magnification.
Image transmitters comprising bundled gradient index optical fibers are known in the art. U.S. Pat. No. 3,658,407 describes a light conducting fiber made of glass or synthetic resin which has a refractive index distribution in a cross section thereof that varies parabolically outward from a center portion thereof. Each fiber acts as a focusing lens to transmit part of an image of an object placed near one end. An assembly of fibers, in a staggered two-row array, transmit and focus an image of the object. The fiber lenses are produced under the trade name "SELFOC"; the mark is registered in Japan and owned by Nippon Sheet Glass Co., Ltd..
Numerous techniques are known in the art for manufacturing glass or plastic fibers with index-of-refraction variations. These are usefully summarized in an article entitled "Gradient Index Optics: a review" by Duncan T. Moore, Applied Optics, Apr. 1, 1980, Volume 19, No. 7, pp. 1035-1038.
Gradient index lens arrays have found wide acceptance as a replacement for conventional image transmitting components in copiers as disclosed, for example, in U.S. Pat. Nos. 3,947,106 and 3,977,777.
Also known in the art are other types of fiber optics image transmitters where the fiber optics essentially act as light pipes. Such a system is disclosed in U.S. Pat. No. 4,194,827 (Bleeker et al.). In this type of imaging system, the ends of the image transmitter are in vertical contact with the document and imaging plane and light is transmitted by multiple internal reflection along the fiber lengths. In Col. 3 of the '827 patent is a suggestion that a single image transmitter could be utilized to produce an enlarged or reduced image by providing a differential rate of movement of the original and receptor surface.
Each of the prior art references related to gradient index lenses discloses a single gradient index lens array transmitting images at a magnification of 1:1. A gradient index lens array that transmits images at other than unity magnification has been disclosed in copending U.S. Application Ser. No. 151,994published as EPO Publication 0040548, assigned to the same assignee as the present invention. In this application were disclosed various reproduction systems which could utilize the nozel gradient index lens array disclosed therein. One embodiment discloses a plurality of gradient index lens arrays, constructed according to the invention, each lens array capable of transmitting to an image plane at a specific magnification. While this type of system is satisfactory for systems requiring only one or two discrete magnification changes, it would be desirable to extend this magnification range without the attendant expense of introducing additional lens arrays.
The present invention is therefore directed to an imaging system for a multi-magnification copier wherein a document on an object plane is reproduced on a photosensitive image plane at a selected magnification, the imaging system including a gradient index lens array assembly comprising: a first gradient index lens array positioned between the object and image plane, to transmit an image of said document onto said image plane at a first magnification; at least a second gradient index lens array positioned between the object and image planes, said lens array adapted to transmit an image of said document onto said image plane at a second magnification; means for illuminating a narrow longitudinal strip of said document; means for providing relative movement between document, lens array assembly and image plane, so as to scan the document at the selected magnification; means for preventing transmission of said document image through a selected one of said lens arrays whereby light reflected from said document is transmitted through said other array at the particular magnification onto the image plane; and means for varying said relative movement, at a selected magnification, so as to anamorphically enlarge or reduce the exposed image at said image plane.